This invention relates to ultrasonic diagnostic imaging systems and, in particular, to the use of ultrasonic diagnostic imaging systems to image the coronary arteries.
Early detection of coronary artery disease is important for the treatment and prevention of myocardial infarction, the primary cause of death of adults in the world. One of the principal methods of detection of coronary artery disease at present is the diagnostic angiogram. An angiogram is acquired by injecting a radiopaque dye into the vascular system, usually by means of a catheter. The radiopaque dye infuses the coronary arteries, and a radiological projection is made of the infused arteries onto a radiographic sensor. The resultant angiogram will reveal the lumens of the arterial vessels of the heart as the radiopaque dye flows through them. A narrowing of the infused lumen will provide an indication of an obstruction of a vessel and a potential condition for infarction.
Ultrasound has been considered as a possible modality to use for coronary artery examinations, which would have the advantage of eliminating the exposure of the patient to the radiation used to form the angiogram, to radiopaque dyes, and the surgical catheterization procedure. However, ultrasonic imaging has its own limitations. One is that the major coronary arteries are located on the irregularly curved surface of the heart and traverse tortuously along the epicardial surface of the heart. Thus, the coronary arteries cannot be viewed in a single image plane, the most prevalent way ultrasonic imaging is done. Furthermore, imaging of the coronary arteries is impeded by the rib cage, which largely blocks ultrasound, and by the motion of the heart itself. Thus, even when a portion of the coronary arteries is accessible to ultrasound, the images of the coronaries are likely to be fleeting, blurred, and of relatively poor resolution.
In accordance with the principles of the present invention, a technique and apparatus are provided for ultrasonically imaging the coronary arteries. The technique includes the use of an ultrasonic contrast agent to sharply reveal the coronary arteries against their background of the myocardium and the lungs, even when the heart is in motion. The apparatus includes a three dimensional ultrasonic imaging system which is capable of scanning a three dimensional volume which includes at least a portion of the coronary arteries. In one display format the three dimensional volume including a coronary artery is projected onto a display plane to produce an ultrasonic image in the same manner as an angiogram. In another display format the three dimensional volume is displayed together with a realtime two dimensional image of a plane of the three dimensional volume. In another display format the bloodflow path of a coronary artery is displayed in a separate, xe2x80x9cstraightenedxe2x80x9d rendering of the vessel.
Conventional radiological arteriograms only detect a few branches down the arterial tree from the major coronary trunks. Ultrasound is capable of also visualizing transmural arteries. Thus, the present invention has the potential of providing visualization of vessels not seen with conventional angiography.